Liquid metal interconnects

ABSTRACT

Embodiments of the invention provide methods for forming electrical connections using liquid metals. Electrical connections that employ liquid metals are useful for testing and validation of semiconductor devices. Electrical connections are formed between the probes of a testing interface and the electronic interface of a device under test through a liquid metal region. In embodiments of the invention, liquid metal interconnects are comprised of gallium or liquid metal alloys of gallium. The use of liquid metal contacts does not require a predetermined amount of force be applied in order to reliably make an electrical connection.

BACKGROUND OF THE INVENTION

Field of the Invention

The embodiments of the invention relate generally to integrated circuitdevices, and more specifically to testing and validation ofsemiconductor chips, testing systems for semiconductor chips, liquidmetal interconnects, and liquid metal alloys.

Background Information

The push for ever-smaller integrated circuits (IC) places enormousperformance demands on the techniques and materials used to constructand test IC devices. In general, an integrated circuit chip is alsoknown as a microchip, a silicon chip, a chip, or a die. IC chips arefound in a variety of common devices, such as the microprocessors incomputers, cars, televisions, CD players, and cellular phones. Aplurality of IC chips are typically built on a wafer (for example, athin silicon disk, having a diameter of 300 mm) and after processing thewafer is diced apart to create individual chips (dies or dice).

As part of the manufacturing process, dies are tested to confirm thefunctioning of the die and provide feedback for the manufacturingprocess. Testing complex semiconductor dies under controlled electrical,thermal, and mechanical conditions in a cost-effective manner presentschallenges as the size of IC chips shrinks and the number of featuresassociated with an individual chip increases.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-D illustrate methods for forming electrical connections betweena testing interface and a device under test.

FIGS. 2A-C illustrate additional methods for forming electricalconnections between a testing interface and a device under test.

FIGS. 3A-B provide schematic diagrams illustrating a cross-sectionalview of probes that are useful for testing electronic devices.

FIGS. 4A-B describe methods for forming electrical connections usingliquid metals.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide interconnects that areuseful for example, for the testing and validation of semiconductordevices. In embodiments of the invention, the interconnects are capableof delivering high currents, such as, currents larger than 1 A, andtesting devices presenting interfaces with feature pitches of less than90 μm. In embodiments of the invention, interconnects are comprised ofgallium or liquid metal alloys of gallium. The use of liquid metalcontacts does not require that a predetermined amount of force beapplied between the testing interface and the device being tested inorder to reliably make an electrical connection. By not applying amechanical force during the formation of electrical connections for chiptesting and validation, mechanical stresses on the solid members of thetesting and validation system (such as the device under test) can bedecoupled.

Embodiments of the invention are useful for high temperature testing andvalidation (“hot sort”) and whole wafer level sort. Hot sort testing isimportant because certain device failures can be caught at highertemperatures.

FIGS. 1A-D illustrate methods for forming electrical connections betweena testing interface and a device under test. The device under test 105is, for example, a packaged or an unpackaged die, a wafer or portion ofa wafer, prepackaged wafer, or any IC interface where a dense array ofelectrical contacts (e.g., having a pitch of less than 90 μm) needs tobe probed. The illustration of the device under test 105 is of a smallregion of the device that presents two electrical interface regions 110,however, an actual device under test 105, such as a die or a wafertypically comprises a large number of electrical interface regions 110,such as, for example tens of thousands to tens of millions for a die ora wafer, respectively. In the cut-away view of the device under test,electrical interface regions 110 are connected to electronic circuitry(not shown) within the interior of the device under test 105. Othershapes and or sizes are possible for the electrical interface regions110, and these regions can also be regions, such as, for example,through-silicon vias (TSVs), bumpless build up layers (BBULs), packageon package (PoP) contacts, and or contacts associated with other methodsof 3-dimensional chip stacking. Embodiments of the invention are notlimited to a particular type of electrical interface region for thedevice under test.

In FIG. 1B, a non-conducting material 115 is deposited on the deviceunder test 105 and patterned. The non-conducting material 115 is, forexample, a photoresist material, SiO₂, SiN, or SiON, or other insulatingmaterial that can be patterned. The patterning of the non-conductingmaterial 115 creates containment regions 120 that are capable ofcontaining a liquid that makes contact with electrical interface regions110. Deposition and patterning occurs through, for example, standardsemiconductor processing techniques. Containment regions 120 are wellsor recesses, for example.

In FIG. 1C, a liquid metal 125 is placed in containment regions 120. Inembodiments of the invention, the liquid metal 125 is gallium metal oran alloy of gallium metal, such as, for example, alloys of gallium andindium, eutectic alloys of gallium, indium, and tin, and eutectic alloysof gallium, indium, and zinc. In general the liquid metal is a metal ormetal alloy that is liquid at the deposition and measurementtemperature. The liquid metal 125 is capable of making electricalcontact with the proximate electrical interface region 110. Inembodiments of the invention, the liquid metal 125 is applied to thedevice under test 105 of FIG. 1B as a liquid metal particle emulsion. Aliquid metal particle emulsion is a mixture of metal micro-particles anda solvent, solvents, or a solvent or solvents and one or moresurfactants. In embodiments of the invention, the solvent is a liquidalkane, alcohol, polyether, or polyol. The solvent is liquid underdeposition temperatures. The solvent is, for example, hexane, isopropylalcohol, hexadecane with a surfactant, such as, oleylamine, Triton(non-ionic surfactant commercially available from Dow Chemical Co.),hexadecyl trimethyl ammonium bromide (HTAB), polyoxyethylene2-oleylether; dimethyl formamide with a surfactant, such as, 1,10 decanedicarboxylic acid, dioctyl phosphate with a surfactant, such as,sulfosuccinate, dipoly ethylene glycol p-nonyl phenyl phosphate with asurfactant, such as, sulfosuccinate, and mixtures thereof. Inembodiments of the invention, the liquid metal particle and solventmixture is created by sonicating the liquid metal in the solvent until acolloidal micro-particle mixture is created. In embodiments of theinvention, the colloidal mixture is comprised of liquid metalmicro-particles having diameters of less than 100 μm. In additionalembodiments of the invention the liquid metal micro-particles exhibit anaverage diameter of between 4 and 55 um or between 4 and 15 μm. Liquidmetal particle emulsions according to embodiment of the invention werefound to be capable of reliably filling well regions having a pitch ofless than 40 μm. In embodiments of the invention, the liquid metalparticle emulsion is converted into a paste-like substance, whichcontains mainly the liquid metal (e.g., the liquid metal particleemulsion comprises 70 to 90% liquid metal and less than 20% solvent)through, for example, a gravity-driven settling process or throughcentrifugation. However, in alternate embodiments of the invention, nosolvent (or solvent-surfactant mixture) is used in the liquid metal.

The liquid metal 125 fills the regions 120. The liquid metal mixture orliquid metal itself is applied to the surface of the device under test105 and excess liquid metal (the material remaining above thecontainment regions 120) is removed. The excess liquid metal can beremoved, for example, by using a squeegee to wipe the surface of thenon-conducting material 115. Any solvent used in the liquid metal isremoved, for example, by evaporation.

In FIG. 1D, a testing interface 130 comprising probes 135 is alignedwith the device under test 105 and the probes are touched down into theliquid metal 125 in containment regions 120. The testing interface 130can also be called a probe card or a sort interface unit. The testinginterface 130 is shown in FIG. 1D as having two probes 135 forsimplicity of illustration, however, a typical testing interfacecomprises a large number of probes for forming electrical connectionswith electrical interface regions presented by devices to be tested.Other shapes are also possible for the probes 135 and the invention isnot limited to a particular probe design. The probes 135 are capable ofmaking an electrical connection with the liquid metal region 125 whichis capable of making an electrical connection with the proximateelectrical interface region 110. An electrical connection between thetesting interface 130 and the electrical interface region 110 is formedthrough the liquid metal region 125. Advantageously, no pressure needsto be applied to the device under test 105 in order to make theelectrical connection with the testing interface 130. The device undertest 105 is then electronically tested and the testing interface 130 ismoved away from the device under test 105.

Although the probes associated with testing interfaces typically havespring-like mechanisms in order to regulate the amount of pressureapplied to a device under test, in embodiments of the invention, nospring-like mechanisms are necessary and the probes 135 used for testingcan be non-flexing members. However, flexible probes can also be used inembodiments of the invention. In embodiment of the invention probes 135are comprised of a conducting material, such as, W, NiW, NiMn, NiCo, Rh,Cu, BeCu, Paliney 7 (a palladium alloy comprising, silver, gold, copper,platinum, and zinc), Au, Ag, Pd, nanocarbon composites, metal coatedsilicon, and or other metals, metal alloys, and composites. Testing ofelectronic devices can be done at a variety of temperatures, such as forexample low temperature, such as −10° C. to 0° C., room temperature, andhigh temperature, such as 90° C. to 100° C., or other temperaturescommonly used to test electronic devices after manufacture. It wasdemonstrated that a 20-50 μm liquid metal (such as gallium alloy) bridgecan carry currents of at least 2 A.

After testing is completed, the testing interface 130 is moved away fromthe device under test 105. The liquid metal 125 is removed and thenon-conducting material 115 is also optionally selectively removed. Theresulting structure, after the removal of both the liquid metal 125 andthe non-conducting material 115 is the structure shown in FIG. 1A.Liquid metal 125 can be removed, for example, through the use ofsolvent-based or acid-based wet methods, sonication, and or dry physicalmethods, such as, for example, excimer lasers. The non-conductingmaterial 115 is removed through standard semiconductor processingtechniques depending on the composition of the layer. In alternateembodiments, the non-conducting material 115 is left in place andserves, for example, as a solder resist opening or a buffer coat layer.

FIGS. 2A-C illustrate additional methods for forming electricalconnections between a testing interface and a device under test. In FIG.2A, a testing interface 205 has probes 210. The testing interface 205can also be called a probe card or a sort interface unit. The testinginterface 205 is shown in FIG. 2A as having two probes 210 forsimplicity, however, a typical testing interface comprises a largenumber of probes for forming electrical connections with electricalinterface regions presented by devices to be tested. Other shapes arealso possible for the probes 210 and the invention is not limited to aparticular probe design. The testing interface 205 is aligned with oneor more reservoirs 220 that contain liquid metal 225. In embodiments ofthe invention, the liquid metal 225 is gallium metal or an alloy ofgallium metal, such as, for example, alloys of gallium and indium,eutectic alloys of gallium, indium and tin, and eutectic alloys ofgallium, indium, and zinc. In general the liquid metal is a metal ormetal alloy that is liquid at the deposition and measurementtemperature. In embodiments of the invention, the liquid metal 225 is aliquid metal particle emulsion. A liquid metal particle emulsion is amixture of metal micro-particles and a solvent, solvents, or a solventor solvents and one or more surfactants. In embodiments of theinvention, the solvent is a liquid alkane, alcohol, polyether, orpolyol. The solvent is liquid under deposition temperatures. The solventis, for example, hexane, isopropyl alcohol, hexadecane with asurfactant, such as, oleylamine, Triton (non-ionic surfactantcommercially available from Dow Chemical Co.), hexadecyl trimethylammonium bromide (HTAB), polyoxyethylene 2-oleylether; dimethylformamide with a surfactant, such as, 1,10 decane dicarboxylic acid,dioctyl phosphate with a surfactant, such as, sulfosuccinate, dipolyethylene glycol p-nonyl phenyl phosphate with a surfactant, such as,sulfosuccinate, or mixtures thereof. In embodiments of the invention,the liquid metal particle and solvent mixture is created by sonicatingthe liquid metal in the solvent until a colloidal mixture is created. Inembodiments of the invention, the colloidal mixture is comprised ofliquid metal micro-particles having diameters of less than 100 μm. Inadditional embodiments of the invention the liquid metal micro-particlesexhibit an average diameter of between 4 and 55 um or between 4 and 15μm. In embodiments of the invention, the liquid metal particle emulsionis converted into a paste-like substance, which contains mainly theliquid metal (e.g., the liquid metal particle emulsion comprises 70 to90% liquid metal and less than 20% solvent) through, for example, agravity-driven settling process or through centrifugation. However, inalternate embodiments of the invention, no solvent (or solvent andsurfactant mixture) is used in the liquid metal 225.

The testing interface 205 is translated toward the one or morereservoirs 220 that contain liquid metal 225. The ends of the probes 210of the testing interface 205 are partially immersed in the liquid metal225. The testing interface is then translated away from the one or morereservoirs 220 forming droplets 227 of liquid metal 225 (shown in FIG.2B) on the ends of probes 210. Any solvent used in the liquid metal 227is evaporated.

In FIG. 2B, the testing interface 205 is moved into position above adevice under test 230 and the probes 210 are aligned with electricalinterface regions 235 of the device under test 230. The device undertest 230 is, for example, a packaged or an unpackaged die, a wafer orportion of a wafer, prepackaged wafer, or any other dense array ofelectrical contacts (e.g., having a pitch of less than 90 μm) that needsto be probed. The illustration of the device under test 230 is of asmall region of the device that presents two electrical interfaceregions 235, however, an actual device under test 230, such as a die ora wafer typically comprises a large number of electrical interfaceregions 235, such as, for example tens of thousands or tens of millionsfor a die or a wafer, respectively. In the cut-away view of the deviceunder test, electrical interface regions 235 are connected to electroniccircuitry (not shown) within the interior of the device under test 230.Other shapes and or sizes are possible for the electrical interfaceregions 235, and these regions might also be regions, such as, forexample, through-silicon vias (TSVs), bumpless build up layers (BBULs),package on package (PoP) contacts, and or contacts associated with othermethods of 3-dimensional chip stacking. As mentioned previously,embodiments of the invention are not limited to a particular type ofelectrical interface region for the device under test.

In FIG. 2C, the testing interface 205 is translated toward the deviceunder test 230 until each droplet 227 makes contact with an electricalinterface region 235. An electrical connection between the testinginterface 205 and the electrical interface region 235 is formed throughthe liquid metal droplet 227. Advantageously, no pressure needs to beapplied to the device under test 230 in order to make an electricalconnection with the probes 210 of testing interface 205. The deviceunder test 230 is then electronically tested and the testing interface205 is moved away from the device under test 230.

Although the probes associated with testing interfaces typically havespring-like mechanisms in order to regulate the amount of pressureapplied to a device under test, in embodiments of the invention, nospring-like mechanisms are necessary and the probes 210 used for testingcan be non-flexing members. In embodiment of the invention probes 210are comprised of a conducting material, such as, W, NiW, NiMn, NiCo, Rh,Cu, BeCu, Paliney 7 (a palladium alloy comprising, silver, gold, copper,platinum, and zinc), Au, Ag, Pd, nanocarbon composites, metal coatedsilicon, and or other metals, metal alloys, and composites. However,flexible probes can also be used in embodiments of the invention.Testing of electronic devices can be done at a variety of temperatures,such as for example low temperature, such as −10° C. to 0° C., roomtemperature, and high temperature, such as 90° C. to 100° C., or othertemperatures commonly used to test electronic devices after manufacture.

The testing interface 205 is then translated away from the device undertest 230. The surface of the device under test 230 is optionallycleaned. Any residual liquid metal 227/225 remaining on the device undertest 230 can be removed, for example, through the use of solvent-basedor acid-based wet methods, sonication, and or dry physical methods, suchas, for example, excimer lasers. In an embodiment of the invention,liquid metal 227 is removed from the ends of the probes 210 and theprocess of FIGS. 2A-C is repeated to probe a second device under test.As mentioned above, liquid metal 227 can be removed, for example,through the use of solvent-based or acid-based wet methods, sonication,and or dry physical methods, such as, for example, excimer lasers. Theliquid metal 227 can be removed, for example, by sonicating the tips ofthe probes 210 in a solvent, such as isopropyl alcohol. In alternateembodiments, the liquid metal 227 on the tips of the probes 210 is notremoved and the process of FIGS. 2A-C is repeated to probe a secondelectronic device. In further alternate embodiments, the liquid metal227 on the tips of the probes 210 is not removed and the testinginterface 205 is translated into position above a second device undertest (not shown) and the second device under test is electronicallytested. In embodiments of the invention, the liquid metal 227 on thetips of the probes 210 may be cleaned after testing a certain number ofdevices and the process of FIGS. 2A-C repeated.

FIGS. 3A-B provide probe designs that are useful in embodiments of theinvention. In FIG. 3A, a testing interface 305 comprises probes 310.Probes 310 have through-holes 315 having a circular aspect. In FIG. 3Btesting interface 325 comprises probes 330. Probes 330 havethrough-holes 335 having a rectangular aspect. In FIGS. 3A-B, thetesting interfaces 305 and 325 can also be called a probe card or a sortinterface unit. The testing interfaces 303 and 325 are shown as havingtwo probes 310 and 330 for simplicity, however, a typical testinginterface comprises a large number of probes for forming electricalconnections with electrical interface regions presented by devices to betested. Other shapes are also possible for the probes 310 and 330. Inembodiments of the invention, probes 310 and 330 are comprised of aconducting material, such as, W, NiW, NiMn, NiCo, Rh, Cu, BeCu, Paliney7 (a palladium alloy comprising, silver, gold, copper, platinum, andzinc), Au, Ag, Pd, nanocarbon composites, metal coated silicon, and orother metals, metal alloys, and composites. Probes having through-holesare useful, for example, in embodiments of the invention in which theprobes are partially immersed in liquid metal and liquid metal dropletsadhere to the ends of the probes when the probes are pulled from theliquid metal, such as those described with respect to FIGS. 2A-C. Ingeneral, probes used in embodiments of the invention employing liquidmetal to form electrical contacts do not need to be as strong as probesused in applications where a pressure is exerted between the deviceunder test and the testing interface. In embodiments of the invention,probes exhibit low resistance and heat tolerance at micrometer pitches.

FIGS. 4A-B describe methods for forming electrical connections usingliquid metals. In FIG. 4A, an insulating material is deposited on adevice to be tested and patterned. The device to be tested is anintegrated circuit chip or a wafer comprising a plurality of integratedcircuit chips, as described more fully herein. The patterning createswells around the electrical interface regions of the device under test.The wells are filled with a metal or metal alloy that is liquid at thedeposition and measurement temperatures. In embodiments of theinvention, the liquid metal comprises gallium or alloys of gallium. Theprobes of a testing interface are inserted into the liquid metal in thewells. A plurality of probes are used and aligned with the plurality ofelectrical interface regions to be probed and present on the deviceunder test and one probe makes electrical contact with one electricalinterface on the device. The probes make electrical contact with theelectrical interface regions through the liquid metal. The device undertest is then electronically tested using a computer system attached tothe testing interface. As described herein, the testing interface isthen translated away and the surface of the device under test is thencleaned to remove the liquid metal and optionally the patternedinsulating layer.

In FIG. 4B, the ends of the probes of a testing interface are insertedinto a reservoir containing a liquid metal. The liquid metal is a metalor metal alloy that is liquid at the deposition and measurementtemperatures. In embodiments of the invention, the liquid metalcomprises gallium or alloys of gallium. The probes are removed from theliquid metal creating droplets of liquid metal on the ends of theprobes. The droplets of liquid metal are contacted with the electricalinterface regions of a device under test. A plurality of probes are usedand aligned with the plurality of electrical interface regions presenton the device under test and one probe makes electrical contact with oneelectrical interface on the chip. The probes make electrical contactwith the electrical interface regions through the liquid metal droplets.The device under test is then electronically tested using a computersystem attached to the testing interface. As described herein, thetesting interface is then translated away and the surface of the deviceunder test is then cleaned to remove the liquid metal.

In general, a testing interface is an interface between a device to betested and a computing system. The computing system comprises a testingcomponent capable of directing the electronic testing of semiconductordevices such as integrated circuit chips and or wafers comprisingintegrated circuit chips. The testing component may have combinations ofhardware components and software components. In some cases, theconnection of one component to another may be a close connection wheretwo or more components are operating on a single hardware platform. Inother cases, the connections may be made over network connectionsspanning long distances.

A computer includes a processing system, including a processor that iscommunicatively coupled to one or more volatile or non-volatile datastorage devices, such as random access memory (RAM), read-only memory(ROM), mass storage devices such as serial advanced technologyattachment (SATA) or small computer system interface (SCSI) hard drives,and or devices capable of accessing media, such as floppy disks, opticalstorage, tapes, flash memory, memory sticks, CD-ROMs and or digitalvideo disks (DVDs). The term ROM refers to non-volatile memory devicessuch as erasable programmable ROM (EPROM), electrically erasableprogrammable ROM (EEPROM), flash ROM, and or flash memory. The processormay also be communicatively coupled to additional components, such asvideo controllers, SCSI controllers, network controllers, universalserial bus (USB) controllers, devices capable of supply data and otherinputs, and user input devices, such as keyboards, touch pads, touchscreens, joysticks, and mice. Communications between elements of thecomputer system, additional processors, and or the electrical usagemonitors can occur using various wired and or wireless short rangeprotocols including, USB, WLAN (wireless local area network), radiofrequency (RF), satellite, microwave, Institute of Electrical andElectronics Engineers (IEEE) 802.11, Bluetooth, optical, fiber optical,infrared, cables, and lasers.

Persons skilled in the relevant art appreciate that modifications andvariations are possible throughout the disclosure as are combinations ofand substitutions for various components shown and described. Referencethroughout this specification to “one embodiment” or “an embodiment”means that a particular feature, structure, material, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the invention, but does not necessarily denote that theyare present in every embodiment. Furthermore, the particular features,structures, materials, or characteristics may be combined in anysuitable manner in one or more embodiments. Various additional layersand or structures may be included and or described features may beomitted in other embodiments.

We claim:
 1. A method for testing a die, the method comprising:providing a die to be tested comprising a surface, wherein the surfacecomprises an insulating material disposed thereon and electricalinterface regions to be used for testing, and wherein the insulatingmaterial comprises wells wherein the electrical interface regions areeach located in a well; placing a liquid metal into the wells on the dieto be tested; forming an electrical connection between probes of atesting interface and the electrical interface regions by contacting theprobes of the testing interface with the liquid metal that is in thewells on the die to be tested; and electrically testing the die to betested after forming the electrical connection between the probes of thetesting interface and the electrical interface regions.
 2. The method ofclaim 1 wherein the insulating material is a photoresist material. 3.The method of claim 1 wherein the liquid metal is comprised of gallium.4. The method of claim 1 wherein the liquid metal is an alloy of galliumselected from the group consisting of alloys of gallium and indium,alloys of gallium, indium and tin, and alloys of gallium, indium, andzinc.
 5. The method of claim 1 wherein the liquid metal is a liquidmetal emulsion.
 6. The method of claim 1 wherein the liquid metal is aliquid metal emulsion and the solvent is selected from the groupconsisting of liquid alkanes, liquid alcohols, liquid polyethers, andliquid polyols.
 7. The method of claim 1 wherein the liquid metal is aliquid metal emulsion having metal micro-particles with an averagediameter between 4 μm and 100 μm.
 8. The method of claim 1 whereinforming an electrical connection between probes of a testing interfaceand the electrical interface regions occurs without the application ofpressure between the testing interface and the die to be tested.
 9. Themethod of claim 1 wherein electronically testing occurs through acomputer operably connected to the testing interface.
 10. The method ofclaim 7 also including removing the liquid metal and photoresistmaterial from the die to be tested after electronically testing the dieto be tested.
 11. The method of claim 1 also including removing theliquid metal and the insulating material.
 12. The method of claim 1,wherein the die to be tested is a packaged die.
 13. The method of claim1, wherein the die to be tested is a portion of a wafer.